1. Field of the Invention
The invention relates to a semiconductor wafer having improved edge region quality, and to a process for producing such a semiconductor wafer.
2. Background Art
The quality demands imposed on the edge of a semiconductor wafer are ever increasing, in particular for large semiconductor wafer diameters (diameter≧300 mm). In particular, the edge of the semiconductor wafer should, as far as possible, be free of contamination and have a low roughness. Moreover, it should be able to withstand high mechanical stresses during handling.
The untreated edge of a semiconductor wafer which has been processed from a single crystal has a relatively rough and uneven surface. Spalling often occurs under mechanical loading, and consequently the wafer represents a source of contaminating particles. It is therefore customary to regrind the edge in order thereby to eliminate spalling and damage in the crystal and to provide it with a specific profile.
Suitable grinding equipment is known from the prior art. It is customary for the semiconductor wafer to be fixed on a rotating table and for its edge to be moved against the rotating working surface of a machining tool. The machining tools used are generally in the form of disks which are secured to a spindle and have circumferential surfaces serving as working surfaces for machining the edge of the semiconductor wafer. The material-removing abrasive grain is usually securely anchored in the working surfaces of the machining tools. These machining tools are suitable for providing the semiconductor wafer with a rounded edge. It is usual for a certain minimum roughness to remain on the edge surface after the edge rounding.
In a subsequent machining step, the edge of the semiconductor wafer, which has been ground and treated with an etching medium, is usually polished. For example, the edge of a centrally rotating semiconductor wafer may be pressed against a centrally rotating polishing drum with a defined force (contact pressure). U.S. Pat. No. 5,989,105 discloses an edge polishing process of this type, in which the polishing drum consists of an aluminum alloy covered with a polishing cloth. The semiconductor wafer is usually fixed on a flat wafer holder, known as a chuck. The edge of the semiconductor wafer projects beyond the chuck so that it is freely accessible to the polishing drum.
For process monitoring, after edge polishing, it is customary to perform a visual check of the edges of representative samples of the semiconductor wafers under a microscope. This visual check is for particles, roughness and defects on the edge of the semiconductor wafer. In particular, the edge of the semiconductor wafer is examined for light reflections which are caused by any unevenness. However, such visual checks are unreliable and do not allow a uniform edge quality to be ensured for all semiconductor wafers processed. Furthermore, the visual check is unsuitable for completely and reliably detecting small defects in the edge region of a semiconductor wafer so as to draw conclusions as to possible defective processing procedures.
Furthermore, there are available inspection appliances which only allow inspection of the semiconductor wafer as far as the wafer edge to a peripheral exclusion zone of 3 mm. Most known inspection appliances cannot be used to examine the entire edge region, i.e. both the edge of the semiconductor wafer and the peripheral exclusion zone. By way of example, EP 1348947 A1 discloses an inspection apparatus which can be used to inspect the edge of the semiconductor wafer but not the entire edge region, while DE 10352936 A1 describes an inspection apparatus which allows automatic detection of defects above a certain size in the entire edge region including the peripheral exclusion zone of the semiconductor wafer.